Contractions are short forms which are used very often in spoken English and in informal writing.An apostrophe (') is inserted in place of the letter which is omitted.
I am sorry, I am late.
I’m sorry, I’m late.
He has come to take her books.
He’s come to take her books.
She was late in submitting her assignment, was she not?
She was late in submitting her assignment, wasn’t she?
combining a noun or pronoun + verb
But in the question forms, where there is a pronoun in the middle of the ‘verb’ and ‘not’, the position of the pronoun gets shifted to the end.